**Principal investigators:**
Sandro Stringari, Lev P. Pitaevskii, Franco Dalfovo, Stefano Giorgini, Iacopo Carusotto, Chiara Menotti, Alessio Recati.

**Postdocs:**
Albert Gallemí, Arko Roy, Luca Parisi, Miki Ota and Soumik Bandyopadhyay

**PhD students:**
Donato Romito, Santo Maria Roccuzzo, Matteo Sighinolfi, Nick Keepfer, Daniele Contessi, Kevin Geier

**Main research field:**

- THEORY OF BOSE GASES AND BOSE-EINSTEIN CONDENSATES
- THEORY OF FERMI GASES
- QUANTUM MIXTURES, QUANTUM IMPURITIES, POLARONS
- SUPERFLUIDITY AND SUPERSOLIDITY
- DIPOLAR GASES
- MULTICOMPONENT AND COHERENTLY COUPLED CONDENSATES
- LOW DIMENSIONAL SYSTEM
- MODELS FOR ATOMS IN OPTICAL LATTICES
- TOPOLOGICAL PHASES OF MATTER
- ANALOG MODELS

**Methods:**
Basic tools of statistical mechanics; hydrodynamic equations and models; mean-field approaches
like Gross-Pitaevskii theory, Bogoliubov equations, BCS theory; sum rules; Quantum Monte Carlo;
Bose-Hubbard and Fermi-Hubbard models; Density Matrix Renormalization group; Tensor Networks.

**Recent PhD theses:**

- Miki Ota (2020), Sound propagation in dilute Bose gases
- Luca Parisi (2019), Mixtures of ultracold Bose gases in one dimension: A Quantum Monte Carlo study
- Fabrizio Larcher (2018), Dynamical excitations in low-dimensional condensates: sound, vortices and quenched dynamics
- Giulia De Rosi (2017), Collective oscillations of a trapped atomic gas in low dimensions and thermodynamics of one-dimensional Bose gas
- Alberto Sartori (2016), Dynamical properties of Bose-Bose Mixtures
- Luis A. Peña Ardila (2015), Impurities in a Bose-Einstein condensate using quantum Monte-Carlo methods: ground-state properties
- Giovanni Italo Martone (2014), Static and dynamic properties of spin-orbit-coupled Bose-Einstein condensates
- Zou Peng (2014), Mean-field theory for the dynamics of superfluid fermions in the BCS-BEC crossover
- Hou Yan-Hua (2013), Two-fluid Hydrodynamics of a quasi-1D unitary Fermi gas
- Marco Larcher (2013), Localization and spreading of matter waves in disordered potentials
- Natalia Matveeva (2013), Study of dynamic and ground-state properties of dipolar Fermi gases using mean-field and quantum Monte Carlo methods
- Gianluca Bertaina (2010), Study of Ultracold Fermi Gases in the BCS-BEC Crossover: Quantum Monte Carlo Methods, Hydrodynamics and Local Density Approximation
- Ingrid Bausmerth (2009), Fermi Mixtures: Effects of Engineered Confinements

A supersolid shows both solid and superfluid properties. By rotating it you can clearly
see that the moment of inertia is strongly reduced due to the superfluid irrotational flow.
Even when the global superfluid behaviour diseappers, the moment of inertia shows a reduction
due to the single droplet (local) superfluidity.
We have also characterized the behavior of quantized vortices, focusing on the supersolid regime.
We have found in particular that (i) the angular momentum per particle associated with the vortex line is
smaller than ℏ, reflecting the reduction of the global superfluidity; (ii) the nucleation in
a rotating trap is triggered -- as for a standard condensate -- by the softening of the quadrupole mode;
(iii) many vortices can be arranged into a honeycomb structure, which coexists with the triangular
geometry of the supersolid lattice and persists during the free expansion of the atomic cloud.

References:

S. M. Roccuzzo, A. Gallemì, A. Recati, S. Stringari,
arXiv:1910.08513,
PRL 124, 045702 (2020)

A. Gallemì, S. M. Roccuzzo, S. Stringari, A. Recati,
arXiv:2005.05718

We study the dynamical evolution of an inhomogeneous ultracold atomic gas quenched at different controllable rates through the Bose-Einstein condensation phase transition. We use a stochastic (projected) Gross-Pitaevskii equation. The results are consistent with the predictions of the homogeneous Kibble-Zurek mechanism and, at long evolution times, also with the experimental observations.

References:

I.-Kang Liu, S. Donadello, G. Lamporesi, G. Ferrari, S.-C. Gou, F. Dalfovo, N.P. Proukakis,
arXiv:1712.08074,
Commun. Phys. **1**, 24 (2018)

I-Kang Liu, Jacek Dziarmaga, Shih-Chuan Gou, Franco Dalfovo, Nick P. Proukakis,
arXiv:2004.09642,
Phys. Rev. Research, in press (2020)

We have developed the equivalent of Bogoliubov theory (for weakly interacting Bose gases) for the Bose-Hubbard model, but starting from the Gutzwiller ansatz.
We find that the approach is extremely well suited to calculate the correlations of the systems. The model is benchmarked against the available QMC result.
The approach is very promising in order to calculate dynamical properties of the BH model.
Reference:

F. Caleffi, M. Capone, C. Menotti, I. Carusotto, A. Recati,
arXiv:1910.08513